Young-Kyu Hong

Controlled two-dimensional distribution of nanoparticles by spin-coating method

We demonstrate that the controlled distribution of nanoparticles can be achieved by employing the spin-coating method. The Co and Ag nanoparticles were uniformly distributed on the Si and SiO2 substrates with this method. The particle density was controllable by varying the concentration of colloids. The spatial distribution of the nanoparticles within the patterned area was also shown to be uniform with small boundary effect, which is favorable for current microelectronics technology. We propose that the spin-coating method can be utilized in developing mass production processes for future nanodevices.

Surface morphology of laser deposited diamondlike films by atomic force microscopy imaging

The surface morphologies of diamondlike carbon (DLC) films with atomic force microscopy (AFM) are reported. The films were prepared by laser ablation with tuning power densities range from 3×108 to 1×1010 W/cm2. For power densities above 2×109 W/cm2, the films reveal smooth surfaces with uniform shapes of nanometer sized carbon clusters (sp3 bonding) and retain the surface roughness of the silicon substrate. For power densities below that, graphitic films are formed, and the surface roughness increases with decreasing laser intensity. The present AFM studies confirm that there exists a clear correlation between surface morphologies and the degree of diamondlike qualities.

Growth of carbon nanotubes from Co nanoparticles and C2H2 by thermal chemical vapor deposition

Abstract Carbon nanotubes (CNTs) were grown from Co nanoparticles by thermal chemical vapor deposition using C 2 H 2 , H 2 , and Ar gases. The diameters of CNTs were limited by the sizes of the catalytic Co nanoparticles. From 5 nm Co nanoparticles, very long and straight CNTs with diameters below 5 nm were grown. C 2 H 2 was so effective as the carbon feedstock that the required amount of C 2 H 2 was only 0.1% of the total amount of gases to grow CNTs from 5 nm Co nanoparticles. For 8 nm Co nanoparticles, a long enough pretreatment time was essential in growing dense CNTs.

Electron emission characteristics of diamond like carbon films deposited by laser ablation technique

Abstract Diamond like carbon (DLC) films are deposited on silicon substrates by the pulsed laser ablation technique. The surface morphology of the DLC film, studied by atomic force microscopy (AFM), shows a strong dependence on the power densities of the laser pulses. The degree of diamond-like properties of the films, which were studied using Raman spectroscopy and Auger electron spectroscopy, shows close correlation with the surface morphology. Electron emission characteristics of the films are measured and their correlations with the surface morphology and bonding structure are investigated. Variation of these structural and electron emission characteristics of the films on the deposition conditions such as substrate temperature and flow rate of atomic hydrogen during the process of laser ablation is also studied.

Facile fabrication of 2-dimensional arrays of sub-10 nm single crystalline Si nanopillars using nanoparticle masks.

A simple procedure for the fabrication of sub-10 nm scale Si nanopillars in a 2-D array using reactive ion etching with 8 nm Co nanoparticles as etch masks is demonstrated. The obtained Si nanopillars are single crystalline tapered pillar structures of 5 nm (top) x 8 nm (bottom) with a density of approximately 4 x 10(10) pillars cm(-2) on the substrate, similar to the density of Co nanoparticles distributed before the ion etching process. The uniform spatial distribution of the Si nanopillars can also be patterned into desired positions. Our fabrication method is straightforward and requires mild process conditions, which can be extended to patterned 2-D arrays of various Si nanostructures.

Enhancement of photoluminescence by microdisk formation from Si/Ge/Si single quantum wells

A significant enhancement of photoluminescence (PL) intensity is observed in microdisks of 0.5 and 1 μm diam, which have been fabricated from Si/Ge/Si single quantum wells (SQWs) grown by molecular-beam epitaxy. The three major PL peaks found at 0.972, 0.957, and 0.920 eV are identified as a no-phonon transition of localized exciton, associated transverse-acoustical, and transverse-optical phonon replicas in Si, respectively. It is suggested that the formation of microdisks from the Si/Ge/Si SQWs enhances the intrinsic PL transitions significantly by suppressing the impurity-related ones.

Controlled Growth of Multi-walled Carbon Nanotubes Using Arrays of Ni Nanoparticles

We have investigated the optimal growth conditions of carbon nanotubes (CNTs) using the chemical vapor deposition and the Ni nanoparticle arrays. The diameter of the CNT is shown to be controlled down to below 20 ㎚ by changing the size of Ni particle. The position and size of Ni particles are controlled continuously by using wafer-scale compatible methods such as lithography, ion-milling, and chemical etching. Using optimal growth conditions of temperature, carbon feedstock, and carrier gases, we have demonstrated that an individual CNT can be grown from each Ni nanoparticle with almost 100% probability over wide area of SiO₂/Si wafer. The position, diameter, and wall thickness of the CNT are shown to be controlled by adjusting the growth conditions.